The present invention relates, in general, to Micro-Electromechanical System (MEMS) devices and, more particularly, to manufacturing MEMS devices.
FIG. 1 illustrates a MEMS device 10 manufactured in accordance with a prior art technique referred to as a glass paste wafer capping technique. In this technique, a plurality of MEMS devices 11 (one shown) are manufactured on a device wafer 12 such as a silicon wafer. Independently, a screen print of glass paste is deposited on a second wafer 13, which is commonly referred to as a cap wafer. The glass paste is cured to form spacers 14, which are then aligned and bonded to device wafer 12. The two wafer combination is then diced by sawing into individual devices. A critical limitation of this technique is that the temperature needed to bond the glass spacers to the device wafer ranges from approximately 400 to 500 degrees Celsius (xc2x0 C.). Temperatures this high can easily damage the MEMS device. Another limitation of this technique is that it is relatively complicated due to the use of screen printing and wafer bonding procedures. Complicated processes are typically less cost efficient because of the added complexity and the lower yield of operational devices.
FIG. 2 illustrates a MEMS device 20 manufactured in accordance with a prior art technique referred to as a cap/cavity technique. In this technique, a plurality of MEMS devices 21 (one shown) are fabricated on a device substrate 22, which is then diced into individual or singulated device components. Each individual MEMS component is subsequently attached to a packaging substrate 23. Packaging substrate 23 is typically ceramic in composition to prevent Radio Frequency (RF) losses that are inherent with substrates such as silicon. MEMS device terminals 26 are then coupled to package leads 27 via wirebonds 24. Then, the MEMS device is hermetically encapsulated with a ceramic cap 28.
One limitation of this technique is that each MEMS device is individually handled and bonded to packaging substrate 23. If the sacrificial protective layer separating the upper and lower control electrodes during fabrication is removed prior to handling, the MEMS device becomes extremely fragile and subject to damage during handling and bonding. If the sacrificial protective layer is not removed prior to handling and bonding, the processing becomes much more complicated due to substrate interaction when the sacrificial protective layer is later removed. In either case, the effective yield of the manufacturing process is adversely impacted. Another limitation of the cap/cavity approach is that the upper surface of packaging substrate 23 has many topographic variations which may prevent the creation of a hermetic seal between it and cap 28.
A limitation common to both the glass paste wafer capping technique and the cap/cavity technique is the requirement for wirebonding the MEMS device to external leads. An intrinsic limitation of wirebonding is the parasitic inductance inherent in the wirebond. This parasitic inductance degrades the RF performance of MEMS devices.
Therefore, a need exists to provide a more reliable, cost effective, and robust MEMS device and method of manufacture that overcomes the deficiencies of the prior techniques.